The secretory and absorptive functions of the epididymis appear to play an important role towards sperm maturation. This proposal is aimed at defining which epididymal regions secrete and absorb amino acids into and out of its lumen respectively. Initially, the concentrations of different amino acids will be estimated in the luminal fluid of the testis (seminferous tubule, rete testis), in different epididymal regions (proximal caput, distal caput, corpus, cauda and ductus deferens), in spermatozoa and in blood plasma. Then, utilizing the technique of stopped-flow split- drop microperfusion, the secretion of amino acids will be determined for each epididymal region (proximal and distal caput, corpus and cauda). Further experiments will be directed towards understanding whether the luminal fluid environment plays and important role in the secretion of amino acids into the lumen of different epididymal regions. In this instance, we will determine whether sodium ions, pH, energy-dependence or testicular factors play a role. The absorption of L-glutamate and L-alanine (those amino acids found to decrease in luminal fluid concentration from caput to cauda) from the lumen of different epididymal regions (caput, corpus and cauda epididymidis) will then be studied using the stopped-flow split droplet microperfusion technique. The specificity and sodium-dependence for each amino acid transport system will be studied in detail. The secretion and absorption of different micromolecules, organic solutes and ions produce a specialized microenvironment which appears to be important for sperm maturation, development and survival. A further understanding of the complex interaction between the epididymal epithelium, microenvironment and spermatozoa will provide information fundamental to the development of a male contraceptive and treatment of certain forms of male infertility.